Well I tried various experiments to see if could get the 1.52 sound core to work in 1.54 and vice versa. But sadly too many features were change, removed, and moved around to really make that practical. At this point I'm still not sure if the sound core is the culprit. Although it is pretty high on my list.
The other option... having a 1.51 and 1.53 to choose between has one small problem of incompatible savestates which I fear may confuse some people. Luckily SRAM is still the same. So if I chose to go this route I may have to resort to just making the naming of the savestates different between the two to at least prevent accidental loading of incompatible savestates.
But that does not remove the possibility of user confusion.. "where'd my savestates go?".. doh!
With choosing between audio engines no longer an option, this multi-build idea seems like a pretty good solution.
How would it work exactly? Would one of the builds operate as the main build, while the second build gets loaded only when called upon? If so, it might make sense for the build, which will likely be used the most, to be designated as the main build so most games will load up at normal speed.
I know first hand how disappointing troubleshooting can be. Glad you did it though, because now you have a better idea of what exactly needs done.